This invention relates in general to multiple-piece molds for forming vehicle wheels and in particular to a multiple-piece mold having interchangeable components and a process for forming wheels which utilizes such a mold.
In the past, vehicle wheels typically have been formed entirely from steel. However, wheels formed from light weight metals, such as aluminum, magnesium and titanium, or alloys thereof, are becoming increasingly popular. In addition to weighing less than conventional all-steel wheels, such light weight wheels can be manufactured having a pleasing esthetic shape. Weight savings also can be achieved by attaching a wheel disc formed from a light weight metal alloy to a steel wheel rim.
Light weight wheels are typically formed by casting or forging operations. Conventional casting operations include numerous processes, such as die casting, low pressure injection casting and gravity casting. Conventional casting operations typically utilize a wheel mold formed from a number of pieces. A wheel mold for casting a one piece vehicle wheel defines a mold cavity which includes a rim cavity for casting a rim portion of the vehicle wheel and a disc cavity for casting a disc portion of the vehicle wheel. During a casting operation, molten metal is poured into the mold cavity and flows into the rim and disc cavities. After the metal cools sufficiently to solidify, the mold is opened and a rough wheel casting is removed. The wheel casting is then machined to a final shape. Machining can include turning the outside and inside surfaces of the wheel rim, facing the inboard and outboard wheel disc surfaces and drilling a center pilot hole and mounting holes through the wheel hub.
For high volume production of vehicle wheels, a highly automated gravity casting process is frequently used. Such automated gravity casting processes typically use a casting machine having a plurality of wheel molds mounted upon a moving structure, such as a rotatable carousel. Each wheel mold is indexed past a refractory furnace containing a pool of molten metal. A charge of molten metal is removed from the furnace pool and poured into a gate formed in the mold. The gate communicates with the mold cavity and gravity causes the metal to flow from the gate into the mold cavity, filling the rim and disc cavities. The mold and the molten metal cool as the casting machine indexes the other molds to the refractory furnace for charging with molten metal. Alter a sufficient cooling time has elapsed, the mold is opened and the wheel casting removed. The mold is then closed and again indexed to the refractory furnace to be refilled with molten metal.
Referring now to the drawings, there is illustrated in FIGS. 1 and 2 a typical prior art multiple-piece wheel mold, which is shown generally at 10. The mold 10 is formed from a high temperature resistant metal, such as steel. The mold 10 includes an annular shaped base 11 which supports the other mold members. The base 11 has a base member 12 which is typically formed as a single piece. The base member 12 has an upper surface 13 which is stylistically shaped to form the outboard face of the disc portion of the wheel casting. As shown in FIG. 1, the base 11 also can include a number of mold components which are attached to the base member 12.
The mold 10 further includes a pair of movable side members 15 and 16 which are supported by the base 11. While two side members 15 and 16 are shown in FIG. 1, it will be appreciated that the mold 10 can include more than two side members. The side members 15 and 16 are movable in a horizontal direction in FIG. 1 and can be extended to a closed position, which is illustrated in FIG. 1, or retracted to an open position by a conventional mechanism which, for clarity, is not shown in FIG. 1. The side members 15 and 16 are shown partially retracted in FIG. 2. The side member 16, which is shown on the right in FIG. 1, has a gate 17 formed therein. A plurality of passageways extend from the gate 17 through the inner surface of the right side member 16.
The mold 10 also includes a top core 20 which is disposed between the side members 15 and 16. The top core 20 can be extended and retracted in a vertical direction, as illustrated in FIG. 2, where the top core 20 is partially retracted. Typically, the top core 20 has a central member 21 which is typically formed as a single piece. Similar to the base member 12, the top core 20 has a lower surface 21 which is stylistically shaped to form the inboard face of the disc portion of the wheel casting. As shown in FIG. 1, the top core 20 also can include a number of mold components which are attached to the central member 21.
When the mold 10 is closed, as shown in FIG. 1, the mold 10 defines a mold cavity 25 having a rim cavity 26 for forming the rim portion of the vehicle wheel and a disc cavity 27 for forming the disc portion of the vehicle wheel. The mold cavity 25 communicates with the gate 17 through the passageways formed through the inner surface of the right side member 16. During casting, the gate 17 receives a charge of molten metal for casting the wheel and feeds the charge into the mold cavity 25 filling the rim and disc cavities 26 and 27. Following solidification of the molten metal in the mold cavity 25, the side members 15 and 16 and top core 20 are fully retracted to allow removal of the wheel casting from the mold base 12.
As described above, the casting process allows the wheel disc to be stylized. Increasingly, stylists are designing distinctive wheels for specific vehicles and also for different trim lines of the same vehicle. As also described above, the wheel disc is formed by the cooperation of the stylized lower surface 22 of the top core 20 and the stylized upper surface 13 of the base member 12. Accordingly, a complete mold is typically constructed for each wheel design. For mass production with the automated casting process, a set of complete wheel molds are typically fabricated for each wheel design. The molds arc then stored between production runs of the wheel.